I've seen this test which showed an average gain of 17.39 HP on a
boosted Stang. LT's are a good supporting mod and worth it to a lot of people, I just don't think they're worth it performance wise on
N/A cars. I don't have the skills to install them, so I also have to consider the $500+ a shop charges.
To clarify what I wrote earlier about gains from a new midpipe, of course you need a new one to accommodate LT's. People often change from a catted to an o/r pipe which contributes to the increase in HP.
I have the mod bug, would just rather save for a SC or new 5.0!